JPH08259381A - Pulling up-controlling method for single crystal - Google Patents

Abstract

PURPOSE: To realize an optimum temperature condition for crystal growth by measuring a two-dimensional temperature distribution and its variation with time on the surface of a melt during pulling up of a single crystal in the single crystal producing method pulling up the single crystal from the melt. CONSTITUTION: In pulling up a single crystal molten in a rotating crucible, an optimum growing environment is known by measuring two-dimensional temperature distribution and its variation with time on the surface of the melt and the rotation speed of the crucible, a rotation speed of the single crystal, relative positions of the crucible and a heater, and a heating condition of the heater are controlled by the resultant information. Summaries of melt current in pulling up by a Czochralski method are shown in the figure. The rotating laminar fluid is about axially symmetrical flow at a low speed rotation of the crucible rotation and the surface temperature distribution of the melt surface is also about axial symmetry. When the rotation speed of the crucible is increased, the flow transfers to axial asymmetry and also the temperature distribution becomes asymmetry. Besides, a temperature gradient in the radial direction also exists and an observation of two-dimensional temperature distribution by an image pickup device such as a CCD camera is necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling pulling of a single crystal of a semiconductor such as silicon having a high yield and a high productivity.

[0002]

2. Description of the Related Art The Czochralski method (hereinafter referred to as the CZ method) for pulling a crystal from a solution in a crucible while growing the crystal is widely used as a method for producing a single crystal. This CZ
When a single crystal is to be obtained by the method, for example, a single crystal manufacturing apparatus having a configuration schematically shown in FIG. 1 is used. In such a single crystal manufacturing method, first, raw materials are put in a crucible in the figure, and the raw material is melted by a heater surrounding them.

Then, the seed crystal is lowered from above the solution in the crucible and brought into contact with the surface of the solution. By rotating this seed crystal and pulling it upward while controlling the pulling speed, a single crystal having a predetermined diameter is produced. In the pulling of this single crystal, the melt flow is controlled for the purpose of preventing polycrystallization and deformation of the crystal, controlling the dopant in the crystal, and the concentration distribution of impurities, and the temperature conditions near the crystal growth. , And have optimally controlled the migration phenomena of dopants and impurities in the melt.

Conventionally, there is no method for directly examining the melt flow, and the crystal growth is performed by trial and error by adjusting the operating conditions such as the crucible rotation speed, the crystal rotation speed, the relative position of the crucible and the heater, and the heating condition of the heater. Has obtained an optimal operating environment for. Further, as an auxiliary means for knowing whether a stable crystal growth environment is realized, there is a method of measuring the temperature at a certain point on the melt surface and using the obtained melt surface temperature fluctuation as an index of the crystal growth environment. It was

For example, as shown schematically in FIG. 2, a radiation thermometer was attached above the chamber to measure the temperature at one point on the surface of the melt. By the measurement, the operating conditions were controlled so that the temperature fluctuations would be reduced to some extent.

[0006]

However, much time and labor are required to search for optimum operating conditions by trial and error as described above. Moreover, these conditions will change with the aging of the carbon member in the pulling furnace. Further, there is a problem in the following points that the guideline for stable crystal growth is obtained only by measuring the temperature at one point on the melt surface by the radiation thermometer.

Conventionally, it has been considered that the temperature distribution of the melt in the crucible is axially symmetrical with respect to the rotation axis of the crucible and is stationary. However, recent research by the present inventor has revealed that the temperature distribution in the melt is non-axial and may be indefinite depending on operating conditions such as the crucible rotation speed.
Due to this non-constant, non-axial temperature distribution, a low temperature part and a high temperature part are created in the circumferential direction of the melt, and the low temperature part and the temperature decreasing part move in the crucible rotation direction, so that the crystal growth interface is stable Temperature fluctuation occurs at one point.

If the temperature fluctuation of the melt near the crystal growth interface is large, the crystal becomes polycrystal and the impurities taken into the crystal become uneven. The magnitude of this temperature change depends on the position of the melt to be measured. That is, it is not possible to know a truly stable crystal growth environment by measuring only one point on the melt surface as in the past.

The radial temperature gradient on the melt surface is also an important condition to control. When the temperature gradient in the radial direction on the surface of the melt is extremely small when the shoulder of the crystal is widened, the crystal diameter may suddenly increase and polycrystallize. Further, when the temperature gradient in the radial direction is extremely small during the growth of the straight body portion of the crystal, the crystal may be largely deformed, and the yield or productivity of the crystal is impaired. The radial temperature gradient on the surface of the melt could not be observed by the conventional measurement of one point on the surface of the melt.

Recently, the following three methods have been reported as methods for directly examining the melt flow. (1) A method of predicting the flow of the melt surface from the black stripe pattern on the melt surface seen during pulling (Yamagishi, Fusegawa: Journal of the Japan Society for Crystal Growth VOL17, No3 & 4, 1990). (2) A method of floating a tracer on the surface of the melt and predicting the flow on the surface of the melt from the movement of the tracer (Shiraishi: 93 Spring Season Proceedings Vol. 1, 1a-H6). (3) A tracer having almost the same density as that of the melt is put in the melt, and X-rays are applied to the entire melt to make X of the melt and the tracer.
A method of tracking the movement of the tracer by the difference in the linear transmittance and knowing the flow of the entire melt (K.Kakimoto, M. Eguti, H. Watanabe, J.
Cry-stal Grouth88 (1988) 365).

However, in the method of knowing the melt flow from the black stripe pattern on the surface of the melt, the relationship between the stripe pattern and the melt flow is not yet clear. Further, crystal growth cannot be performed by a method in which a tracer is placed in the melt to know the melt flow. As described above, these methods have a problem to be used in the actual single crystal manufacturing site.

An object of the present invention is to obtain an optimum pulling environment for crystal growth by quickly and in detail grasping the two-dimensional temperature distribution on the surface of the melt and its time variation during pulling of a single crystal. To do.

[0013]

In order to achieve the above-mentioned object, the inventors of the present invention observe the melt surface two-dimensionally and grasp the time fluctuation of the melt surface temperature in detail to obtain stable stability. The inventors have found a method for pulling a single crystal and completed the present invention.

That is, according to the present invention, in the method for producing a single crystal in which a single crystal is pulled from a melt, the two-dimensional temperature distribution on the surface of the melt and its time variation are measured during pulling of the single crystal. It is a method characterized by knowing the growth environment.

Further, according to the present invention, in a single crystal manufacturing method for pulling a single crystal from a crystal member melt melted by a heater in a rotating crucible, the surface of the crystal member melt is pulled during pulling of the single crystal. By measuring the two-dimensional temperature distribution and its time variation, the optimum growth environment of the single crystal is known, and based on this, the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, the heater The single crystal pulling control method is characterized in that the growth environment of the single crystal is controlled with the temperature distribution on the melt surface as an axis by adjusting the heating conditions.

Further, according to the present invention, in a method for producing a single crystal in a rotating crucible for pulling a single crystal from a crystal member melt melted by a heater, the surface of the crystal member melt is pulled during pulling of the single crystal. By measuring the two-dimensional temperature distribution and its time variation, the optimum growth environment of the single crystal is known, and based on this, the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, the heater The single crystal pulling control method is characterized by controlling the heating environment of the single crystal to control the growth environment of the single crystal by reducing the temperature fluctuation at least near the crystal growth interface.

[0017]

According to the present invention, the crystal growth environment is grasped in detail by two-dimensionally determining the melt surface temperature from above the single crystal pulling melt, and the operation guide for obtaining the optimum environment for crystal growth is provided. Can be easily created.

In pulling a single crystal, radiant energy corresponding to the temperature is emitted from the surface of the melt. The relationship between the radiant energy Q and the temperature T is as follows if no other reflection is superposed.

Q = εσT ⁴ where ε is the emissivity of the melt, σ is the Stefan-Boltzmann constant, and T is the melt surface temperature. By measuring this radiant energy two-dimensionally from above and converting it to the temperature according to the above conversion formula or a conversion formula modified to suit the actual system, the melt surface temperature can be known without contact. be able to.

By continuously observing these, it is possible to two-dimensionally know the time variation of the melt surface temperature. The melt surface temperature distribution and temperature fluctuation can be changed by changing the operating conditions such as the crucible rotation speed, the crystal rotation speed, the relative position of the crucible and the heater, and the heating condition of the heater. Therefore, these melt surface temperature data serve as an operation guide for obtaining an optimum operating environment for crystal growth. The method described above has the advantage that even if the members in the furnace change with time, the melt surface temperature can always be observed and the operating conditions can be optimally corrected, so that operation taking into consideration the change with time is possible. .

FIG. 3 shows a schematic view of melt flow in CZ pulling. The characteristic of the melt flow in the CZ pulling is that the melt heated on the crucible side wall rises along the crucible side wall and changes the direction of the flow toward the center axis of the crucible near the free surface. After it sinks near the central axis, it turns at the bottom of the crucible and flows toward the side wall of the crucible. This forms a flow (meridional flow) in the vertical cross section of FIG. Normally, the crucible is rotated when pulling up the CZ. As a result, the flow induced by the rotation of the crucible overlaps the above flow. A fluid that is thus density-stratified (where there is a density difference in the fluid) and that is rotating is called a rotary stratified fluid. A typical example of this is the Earth's atmosphere, which is the melt in CZ pull-up. Liquid flow and the flow of the earth's atmosphere are very similar.

From the temperature measurement experiment and numerical simulation of the present inventor in such a rotary stratified fluid, the following was found.

When the crucible rotation is low, the flow of the rotary stratified fluid is substantially axisymmetric, and the melt surface temperature distribution is also substantially symmetrical (FIG. 3 (a)). However, when the crucible rotation speed was increased, horizontal vortices were generated on the free surface of the melt, and the flow transitioned to a non-axial symmetry. As a result, the temperature distribution on the surface of the melt becomes non-axial.

The axisymmetric distribution moves in the crucible rotation direction at a speed dependent on the crucible rotation speed. Due to this non-axially symmetrical rotation of the temperature distribution, when focusing on one point on the circumference of a certain system on the surface of the melt, the low-temperature melt and the high-temperature melt are periodically moved to that point. To come
At that point, temperature fluctuation occurs based on the temperature difference between the low temperature and high temperature melts. The magnitude and cycle of this temperature fluctuation are different at the radial position of interest, and there is a radial position having the maximum temperature fluctuation amplitude on the melt surface.

Further, the radial position having the maximum temperature fluctuation amplitude changes depending on operating conditions such as the crucible rotation speed. When the crucible rotation is further increased, the flow in the vertical section and the temperature distribution in the horizontal section become as shown in FIG. 3 (c). In this state, even if the temperature distribution is not symmetrical with respect to the axis, a region where the temperature fluctuation is small is formed near the central axis. That is, the maximum portion of the temperature fluctuation moves closer to the crucible than in FIG. 3B.

From the above reason, it is understood that an accurate melt temperature environment cannot be obtained by measuring the temperature of only one point on the melt surface. Further, the temperature gradient in the radial direction on the surface of the melt also changes depending on operating conditions such as the crucible rotation speed. In the present invention,
A two-dimensional temperature distribution on the melt surface is obtained by observing the two-dimensional distribution of the radiant energy emitted from the melt surface with an imaging device such as a CCD camera, converting it into an electric signal, and converting it into temperature. . While transferring this two-dimensional temperature distribution to the display, the crucible rotation speed, crystal rotation speed, crucible position, and heater heating conditions are changed during operation to obtain the optimum state for crystal pulling.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples.

As shown in FIG. 4, the temperature distribution of the melt surface in the absence of crystals was two-dimensionally measured from the upper part of the chamber above the melt with a CCD camera. FIG. 5 shows a schematic diagram of the surface temperature distribution when 45 kg of polycrystalline silicon is melted in an 18 inch crucible and the surface of the melt is observed from above by the above method. The dotted line in the figure indicates the position of the 6-inch crystal single crystal. FIG. 5A shows the temperature distribution at the crucible rotation speed of 2 rpm. The crucible rotation speed 2r is shown in FIG.
The temperature distribution in pm is shown.

The temperature distribution on the surface of the melt is the crucible rotation speed 2r.
At pm, the axis had already transitioned to the asymmetric axis, which was rotating in the crucible rotation direction. The most non-axial symmetry existed just around the edge of the crystal 6 inches from the center of the crucible (Fig. 5 (a)).

Further, the temperature gradient in the radial direction of the melt surface also takes the minimum value at the position where the temperature fluctuation is greatest. As a result of pulling up the 6-inch crystal in this state, almost all of the crystal was polycrystallized in the process of expanding the shoulder of the crystal. On the other hand, FIG.
Even in the state of (b), the temperature distribution on the surface of the melt shows an asymmetric axis, but by increasing the rotation speed of the crucible, the largest temperature fluctuation on the melt surface and the smallest radial part are 6 inches. It moved out of the radius of the crystal, and the crystal pulled up as a single crystal without polycrystallization or deformation.

[0031]

As described above, according to the method of the present invention as set forth in claim 1, the optimum growth environment can be known, and the temperature environment of the surface of the melt can be grasped more reliably than the conventional one-point measurement of the melt surface temperature. Therefore, it can be used as an operation guide for realizing the optimum temperature condition for crystal growth.

According to the single crystal pulling control method of the present invention according to claim 2, the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, and the heating conditions of the heater are adjusted to adjust the melt surface. It is possible to pull a high quality single crystal with the temperature distribution of the above as the axis.

According to the single crystal pulling control method of the present invention as set forth in claim 3, at least the crystal growth interface is adjusted by adjusting the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, and the heating conditions of the heater. High-quality single crystals can be pulled by reducing temperature fluctuations in the vicinity.

[Brief description of drawings]

FIG. 1 is a drawing schematically showing a CZ furnace.

FIG. 2 is a drawing showing a single-point measurement of a melt surface with a radiation thermometer.

FIG. 3 shows a typical flow of melt in CZ pulling,
It is a figure showing the crucible rotation dependence of temperature distribution.

FIG. 4 is a drawing showing two-dimensional temperature measurement of a melt surface by an imaging device such as a CCD camera.

FIG. 5: Crucible rotation and C at 2 rpm and 8 rpm
It is drawing which represented typically the temperature distribution of the melt surface observed by the CD camera.

[Explanation of symbols]

 a ... Crystal b ... Melt c ... Crucible d ... Crucible support e ... Crucible receiver f ... Crucible shaft g ... Heater h ... Insulation material i ... Furnace wall

Claims (3)

[Claims] 1. A method for producing a single crystal in which a single crystal is pulled from a melt, in which an optimum growth environment is obtained by measuring a two-dimensional temperature distribution on the surface of the melt and its time variation during the pulling of the single crystal. A method characterized by knowing. 2. A method for producing a single crystal in a rotating crucible for pulling a single crystal from a crystal member melt melted by a heater, wherein a two-dimensional surface of the crystal member melt is pulled during the pulling of the single crystal. By knowing the temperature distribution and its time variation, to know the growth environment of the single crystal, based on this, the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, A single crystal pulling control method, wherein the growth environment of the single crystal is controlled with the temperature distribution on the melt surface as an axis by adjusting the heating conditions of the heater. 3. A single crystal manufacturing method for pulling a single crystal from a crystal member melt melted by a heater in a rotating crucible, wherein a two-dimensional surface of the crystal member melt is pulled during the pulling of the single crystal. By knowing the temperature distribution and its time variation, to know the growth environment of the single crystal, based on this, the rotation speed of the crucible, the single crystal rotation speed, the relative position of the crucible and the heater, A method for controlling pulling of a single crystal, characterized in that a growth environment of the single crystal is controlled by adjusting a heating condition of the heater to reduce temperature fluctuation at least near a crystal growth interface.